1. Field of the Invention
This invention relates generally to optical detector assemblies for discerning light-dark variations in a surface, and specifically to assemblies utilizing transmitting and receiving waveguides in accomplishing same.
2. Description of Prior Art
Optical detector assemblies for use in facsimile reproduction or the like are generally well-known in the art and typically comprise illuminating waveguide means for illuminating an encoded surface with light, and receiving waveguide means positioned to optimally detect reflected light from reflective areas of the encoded surface. Such optical detector assemblies are commonly incorporated in a light-pen type device intended for movement across the subject encoded surface, or mounted stationary in a fixture beneath which the encoded surface is regularly passed.
Achievement of an ideal optical detector assembly, however, has been illusive to the industry because of the heretofore irreconcilable optical performance and manufacturing demands placed on any proposed detector assembly. One problem in the construction of a satisfactory assembly is to provide sufficient illumination of the subject surface. The designers of optical detector assemblies have attempted to solve this problem by providing detector devices having multiple illuminating waveguides which flood a relatively large portion of the subject surface with transmitted light. An apparatus utilizing this approach is described in U.S. Pat. No. 4,033,698 and comprises a plurality of illuminating waveguides angularly referenced from a receiving waveguide. While this device works well in delivering sufficient illumination to the subject surface and has been well received by the industry, certain shortcomings prevent the apparatus from representing an ideal solution. One shortcoming is that illuminating a large area of the subject surface can negatively affect the resolution of the relatively small portion of that illuminated large area detected by the receiving waveguide. The degradation in resolution is a consequence of fringe illumination entering the receiving waveguide. Further, the manufacture of an optical detector apparatus having multiple illuminating waveguides is relatively difficult and therefore expensive, particularly if the illuminating waveguides are intended to be angularly referenced from the receiving waveguide for enhanced illumination of the subject surface.